Various type chemical processes are commonly carried out in large, stirred vessels which are frequently provided with auxiliary equipment, such as baffles, heat transfer coils which enable heat to be supplied or extracted from the contents of the vessels, and the like. In many cases, however, such processes eventually produce undesirable deposits on the surfaces of the equipment with which the reaction mixtures come into contact. Such deposits interfere with the efficient transfer of heat to and from the interior of the vessels. Further, these deposits have a tendency to deteriorate and to partially fragment resulting in contamination of the reaction mixture and the products produced therefrom. This problem is particularly prevalent in polymerization type reactions, since the deposits, or "build-up," of solid polymer on reactor surfaces, not only interferes with heat transfer, but decreases productivity and adversely affects polymer quality.
This problem is particularly bad in the commercial production of polymers and copolymers of vinyl and vinylidene halides, when polymerized alone or with other vinylidene monomers having a terminal CH.sub.2 =C&lt; group, or with copolymerizable polyolefinic monomers. For example, in the commercial production of vinyl chloride polymers, the same are usually produced in the form of discrete particles by polymerization in aqueous suspension systems. When employing such a polymerization system, the vinyl chloride, and other comonomers when used, are maintained in the form of small discrete droplets by the use of suspending agents and agitation. When the reaction is complete, the resultant polymer is washed and dried. These aqueous suspension system polymerization reactions are usually conducted under pressure in metal reactors equipped with baffles and high speed agitators. However, these suspension systems are inherently unstable and during the polymerization reaction, vinyl chloride polymer builds up on the interior surfaces of the polymerization reactor, including the surfaces of the baffles and agitator. Obviously, this polymer build-up must be removed since it results in further formation of polymer build-up on the reactor surfaces which results in a crust that adversely affects heat transfer and contaminates the polymer being produced.
The nature of the polymer build-up or insoluble deposit on the walls of the reactor is such that in the commercial production of polymers, as described above, it has in the past been standard practice, after each polymerization reaction is completed, to have an operator enter the reactor and scrape the polymer build-up off the walls and off the baffles and agitator. An operation such as this is not only costly, both in labor and down-time of the reactor, but presents potential health hazards as well.
Various methods have heretofore been proposed to reduce the amount and nature of polymer build-up on polymerization reaction surfaces, such as solvent cleaning, various hydraulic and mechanical reactor cleaners, and the like. However, none of these methods has proved to be the ultimate in polymer build-up removal or prevention. That is to say, these various methods and apparatus have done an acceptable job, but there still remained room for improvement in this area, particularly from an economic point of view. As a result, a number of coating compositions have been recommended for use on the inner surfaces of the reactor to reduce build-up. One particularly good coating composition was one comprised predominantly of polyethyleneimine and described by the present applicant in copending application U.S. Ser. No. 391,880, filed on even date herewith, now U.S. Pat. No. 3,849,179. This coating essentially eliminates polymer build-up when employed in a polymerization reactor. However, Applicant did not stop there and has now developed a new process which not only substantially eliminates polymer build-up but presents a substantial improvement over prior art processes and the use of the polyethyleneimine coating per se.